Water vapor permeable thermoplastic polyurethane film

ABSTRACT

Claimed is a non-porous, waterproof film having a water vapor permeability of at least 1000 g/m 2  day, based on a thermoplastic polyurethane, wherein the polyurethane is composed of 
     a) 40 to 52 wt. % of polyether glycol having an atomic ratio of carbon to oxygen in the range of 2,0 to 4,3, with at least 30 wt. % of the polyurethane being composed of a polyether glycol having an atomic ratio of carbon to oxygen in the range of 2,0 to 2,4, 
     b) 30 to 45 wt. % of polyisocyanate, calculated as 4,4′-diphenyl methane diisocyanate, 
     c) 0,5 to 10 wt. % of araliphatic diol, and 
     d) 5 to 20 wt. % of low-molecular weight chain extender, calculated as 1,4-butane diol, less the amount of araliphatic diol. 
     Also claimed is the use of these films in rainwear, shoes, tents, seats, as mattress covers, as understating, in garments for medical purposes, and for the manufacture thereof of wound dressings.

The invention pertains to a non-porous, waterproof film having a watervapour permeability of at least 1000 g/m² day in accordance with ASTME96-66 (Procedure B), with the proviso that the water temperature iskept at 30° C., while the ambient temperature is 21° C. at 60% RH, basedon a thermoplastic polyurethane composed of a polyether glycol, apolyisocyanate, and a chain extender, at a ratio of NCO to activehydrogen atom of 0,9 to 1,2, and to the use of such films in rainwearand tents, as mattress covers, as underslating for roofing, in themanufacture of waterproof shoes, in the manufacture of seats, especiallycar seats, in garments for medical purposes, and for the manufacturethereof of wound dressings.

Non-porous, waterproof and water vapour permeable films based on athermoplastic polyether urethane of the aforesaid composition having awater vapour permeability of at least 1000 g/m² day are known fromJP-A-09 157 409. The preparation of the polyurethane resin does notinvolve the use of solvents. Because of the presence of a very highpercentage of polyethylene oxide glycol, a polymer is obtained which inits film form has a very high water vapour permeability, but which alsohas high tackiness. Furthermore, it was found that the waterproofness offilms of the composition as described in said document is found wantingfor a wide range of applications. Likewise, polyurethanes of thecomposition as described therein generally have a too low melting pointfor use in many of the applications listed above.

The invention now provides non-porous thermoplastic polyurethane filmshaving a high water vapour permeability, a satisfactory waterproofness,and a sufficiently high softening point to allow cleaning at highertemperatures in the case of use in, e.g, garments.

The invention consists in that in a thermoplastic polyurethane film ofthe known type mentioned in the opening paragraph the polyurethane iscomposed of:

a) 40 to 52 wt. % of polyether glycol, calculated as polyethylene oxideglycol, having an average molecular weight of greater than 800 to 4000and an atomic ratio of carbon to oxygen in the range of 2,0 to 4,3, withat least 30 wt % of the polyurethane being composed of a polyetherglycol having an atomic ratio of carbon to oxygen in the range of 2,0 to2,4,

b) 30 to 45 wt. % of polyisocyanate, calculated as 4,4′-diphenyl methanediisocyanate,

c) 0,5 to 10 wt. % of araliphatic diol of the formula

 k=0 or 1, where if k=1, Y stands for a methylene or isopropylidenegroup,

Q has the meaning of an H-atom or a CH₃ group, C₆X₄ has the meaning of aphenylene group wherein X is hydrogen or a chlorine or bromine atom, andm and n may be the same or different and stand for an integer≧1, withm+n≦10, and

d) 5 to 20 wt. % of a chain extender having a maximum molecular weightof 500, calculated as 1,4-butane diol, less the amount of araliphaticdiol.

Surprisingly, it was found that polyurethane films of the aforesaidcomposition are well-balanced in terms of softening point, water vapourpermeability, waterproofness, and sticking. Moreover, using ahalogenated araliphatic diol makes it possible to obtain films whichhave fire retardant properties. It should be noted that thermoplasticpolyurethanes which have a higher softening point because of theincorporation of a compound based on an ethoxylated and/or propoxylatedbisphenol A are known as such from Japanese patent publicationsJP-A-55-54320 and JP-A445117.

The former publication discloses a polyurethane incorporating a compoundof the formula

For the meaning of n and m an integer of 2 to 30 is listed there, whileQ stands for a CH₃ group or a hydrogen atom and C₆H₄ stands for aphenylene group. The examples only mention diols with an averagemolecular weight of 1800 to 2000. The compounds do not have the effectof increasing the softening point, however, but only have a favourableeffect on such general physical properties as resistance to degradationunder the influence of UV light, yellowing, and sticking. Nor is thereany mention of the possible use of polyethylene oxide glycol for themanufacture of water vapour permeable films.

In the latter publication there also is a polyurethane incorporating adiol according to the formula above. The object in this case is toobtain a less brittle polymer which gives fewer injection mouldingproblems. In order to obtain a sufficiently hard polymer, the molecularweight of any polyalkylene oxide glycol incorporated therein should notexceed 800. Consequently, there is no question of the manufacture offilms, let alone waterproof yet at the same time water vapour permeablefilms.

Preferably, the long-chain glycols are composed wholly of polyethyleneoxide glycol. In some cases it may be desirable to employ random orblock copolymers of epoxyethane with minor amounts of a secondepoxyalkane. In general, the second monomer makes up less than 40 mole %of the polyalkylene oxide glycols, preferably less than 20 mole %.Suitable examples of second monomers are 1,2- and 1,3-epoxypropane,1,2-epoxybutane, and tetrahydrofuran. Alternatively, use may be made ofmixtures of polyethylene oxide glycol, e.g., poly-1,2-propylene oxideglycol or polytetramethylene oxide glycol.

Using a polyalkylene oxide glycol with a molecular weight of 800 or lesswill generally be at the expense of the water vapour permeability, andalso less flexible films are obtained. Using a polyalkylene oxide glycolwith a molecular weight of more than 4000 may give rise to problems dueto phase separation.

So far, very favourable results have been obtained using a polyalkyleneoxide glycol with an average molecular weight of 1000 to 3000.

Optimum results have been obtained so far using a polyalkylene oxideglycol with a molecular weight of about 2000.

The amount of polyether glycol may vary within wide limits. In general,optimum results are obtained using a weight percentage between 41 and50.

Depending on the meaning of Q, X, m, and n, the amount of araliphaticdiol varies between 0,5 and 10 wt. %, but preferably between 1 and 8 wt.%.

Very good results were obtained using an araliphatic diol according tothe formula above wherein k=1, Y represents an isopropylidene group, Qand X have the meaning of an H-atom, and m and n=1.

Very good results were also obtained using an araliphatic diol accordingto the formula above wherein k=1, Y represents an isopropylidene group,Q has the meaning of a CH₃ group and X has the meaning of a hydrogenatom, and m and n=1.

The amount of polyisocyanate, calculated as 4,4′-diphenyl methanediisocyanate, is at least 30 and at most 45 wt. %.

Examples of suitable polyisocyanates are 4,4′-diisocyanatodiphenyl,3,3′-dichloro-4, 4′-diisocyanatodiphenyl,3,3′-diphenyl-4,4′-diisocyanatodiphenyl, 3,3′-dimethoxy-4,4′-diisocyanatodiphenyl, 4,4′-diisocyanatodiphenyl methane,3,3′-dimethyl-4, 4′-diisocyanatodiphenyl methane, and adiisocyanatonaphthalene. Optimum results were obtained using an amountin the range of 35 to 42 wt. %, calculated as 4,4′-diphenyl methanediisocyanate.

The amount of low-molecular weight chain extender in the polyurethaneresin is 5 to 20 wt. %, calculated as 1,4-butane diol, less the amountof araliphatic diol according to the formula above. The low-molecularweight chain extending agent preferably has two reactive hydrogen atomsand a molecular weight of at most 500, preferably of at most 300.

Suitable hydroxy-functional compounds include aliphatic orcycloaliphatic polyols having 2 hydroxyl groups. Examples of polyolsinclude ethylene glycol, propylene glycol, diethylene glycol,tetramethylene diol, neopentyl glycol, hexamethylene diol, cyclohexanediol, and bis-(4-hydroxycyclohexyl)methane. Also suitable for use arelow-molecular weight amino acid hydrazides such as aminoacetic acidhydrazide, α-aminopropionic acid hydrazide, β-aminopropionic acidhydrazide, β-amino-α,α-dimethyl amino-propionic acid hydrazide,low-molecular weight diamines such as ethylene diamine, 1,2-propylenediamine, 1,4-butylene diamine, 2,3-butylene diamine, hexamethylenediamine, piperazine, 1,4-diaminopiperazine, toluene diamine, phenylenediamine, diphenyl methane diamine, low-molecular weight hydrazines suchas hydrazine and monoalkyl hydrazine, low-molecular weight dihydrazides,such as adipic acid dihydrazide and terephthalic acid dihydrazide.

The preparation of thermoplastic polyurethanes for use in themanufacture of the waterproof and water vapour permeable films accordingto the invention may take the following form.

First, the diisocyanate is charged to a reactor and heated underanhydrous conditions in a nitrogen atmosphere to a temperature between40 and 100° C., preferably to just above its melting point. Thepolyether glycol, which preferably is at the same temperature as thediisocyanate, is then added dropwise at such a rate that the glycol isblocked completely by isocyanate groups. During the reaction there isheating to such a temperature as will still allow good stirring of thereaction mixture. This temperature generally is in the range of 60 to150° C. The mixture of araliphatic diol and low-molecular weight chainextender is then added with good stirring, the resulting mixture ispoured into a container and, after cooling, cut up and shaped into agranulate, which is then charged to a twin-screw (mixing) extruder inorder to be processed into granules from which films having a thicknessup to the range of 10 to 50 μm can be made in a manner known in the artusing a flat die extruder or a blow moulding extruder. Alternatively,the polyurethane can be prepared by bringing all of the reactioncomponents into contact with each other virtually simultaneously. Inthat case preferably first a mixture of polyalkylene ether glycol andchain extenders is made, which is then added to the polyisocyanate. Thereaction may take place in a reactor, but also in an extruder.Furthermore, it is possible to carry out the process batchwise or whollycontinuously.

Under certain conditions it may be advantageous to carry out thepreparation of the prepolymer in the presence of one or more polarorganic solvents such as dimethyl formamide, dimethyl acetamide, diethylformamide, dimethyl sulfoxide, hexamethyl phosphorus amide,tetramethylene urea, and N-methyl-2-pyrrolidone. After evaporation ofthe solvent and, optionally, further curing of the polymer to the air afilm is obtained with a water vapour permeability which is dependent onthe composition of the polymer as well the thickness of the film. Forevery selected film thickness the water vapour permeability shouldalways be at least 1000 g/m² day. In general, very favourable resultsare obtained using a polymer film with a thickness in the range of 5 to35 μm. Optimum results are obtained using a polymer film of 5 to 20 μmthick.

The preparation on a commercial scale of thermoplastic polyurethanes foruse in the manufacture of the films according to the invention generallyis as follows. The polyol, the chain extender, and the polyisocyanateare fed from separate (stirred) tanks to a mixing device equipped with astirrer and conveyed from there to a twin-screw (mixing) extruder, withcare being taken to ensure that the overall residence time of themixture in the mixing device and the twin-screw (mixing) extruder doesnot exceed 2 to 3 minutes. Next to the extuder there is a granulatorwhich cuts the polymer melt up into processable granules withsimultaneous cooling.

If so desired, a catalyst may be used in the preparation of thepolyurethane, e.g., a tin based catalyst. The amount of it to beincorporated generally ranges from 20 to 2000 ppm, calculated on thetotal of the constituents taking part in the reaction. The temperatureat which the aforesaid addition reactions take place preferably is keptas low as possible in order to prevent the occurrence of objectionableside reactions, which are attended with the formation of allophanate,biuret, and triisocyanate groups. These side reactions cause branchingand/or cross-linking of the polymer, resulting in a deterioration of thephysical properties in general.

During the polyurethane preparation additives, such as pigments,fillers, stabilisers, antioxidants, dyes, and flame extinguishers, maybe added to the reaction mixture at any moment of the preparation.

The manufacture of films from the present polyether urethanes proceedsin a manner known as such from the art, such as described inKirk-Othmer, Encyclopedia of Chemical Technology 9 (1966), pp. 232-241.

Blow moulding extrusion will give films having a thickness in the rangeof 5 to 35 μm.

However, preference is given to flat films obtained by flat dieextrusion on a cooled roller. In that case a roller temperature ofbetween 75 and 185° C., such as is described in U.S. patentspecification U.S. Pat. No. 3,968,183, is preferred. In order to counterthe film's sticking to the roller, generally a “non-blocking” agent isadded, such as microtalc and/or silica, e.g. diatomaceous earth.

If the manufacture of laminates is the main priority, extrusion coating,in which the laminate and the film are produced simultaneously, is alsoan option.

In order to prevent the resulting films from sticking in the end, theobtained flat film is wound together with LDHD polyethylene film.

For the manufacture of waterproof rainwear or tents according to thepresent invention very favourable results are obtained usingpolyurethane films made by flat die extrusion and/or blow mouldingextrusion which have a waterproofness of at most 400 Ml/M²24 hours.

It was found that the polyurethane films according to the invention arealso highly suitable for use in the manufacture of seats, moreparticularly car seats. Films made from a polyurethane incorporating ahalogenated araliphatic diol such as polyoxypropylene(2.4)2,2-bis(4-hydroxy-3,5-dibromophenyl)propane or polyoxyethylene(2.2)2,2-bis(2,3,5,6-tetrabromo-4-hydroxyphenyl)propane have fire retardantproperties and so are pre-eminently suitable for the manufacture ofaircraft seat covers.

Another important application is the manufacture of waterproof shoes,more particularly sports shoes.

A further use made feasible by the films according to the presentinvention is the manufacture of mattress covers. The well-known mattresscovers made of water vapour permeable films based on copolyether estersadmittedly have a high water vapour permeability, but they are notsuitable for recurrent use and hence too expensive for use in hotels,hospitals, and the like on account of the too low resistance ofcopolyether ester films to hydrolytic degradation on repeatedsterilisation. Nor are the well-known films based on copolyether esteramides suitable for use to this end, not only because of the presence ofa readily hydrolysable ester group, but also because of the fact thatthe commercially available films made of these polymers have a too lowmelting point.

The invention will now be elucidated with reference to the followingexamples. These are for illustrative purposes only and are not to beconstrued as limiting the scope of the invention in any way. All partsand percentages mentioned in the application are parts by weight andweight percentages, unless otherwise specified.

The following methods were used to determine the properties of thepolyurethane films and/or the waterproof garments, shoes, tents,mattress covers, and the like made therewith.

A. Determination of the water vapour permeability (WVP) in accordancewith ASTM E96-66 (Procedure B), with the proviso that the watertemperature is kept at 30° C., while the ambient temperature is 21° C.at 60% RH.

B. Determination of the waterproofness (WT) by measuring the amount ofwater in ml/m²24 hours which passes through a film covered on eitherside with water at a differential pressure of 80 kPa.

C. Determination of the permanent plastic deformation (PPD) using themethod specified below.

A 25 mm wide membrane is fixed in a draw bench with a length betweengrips of 50 mm. The strip is elongated 100% at a rate of 100% perminute, which for the aforementioned length between grips corresponds to50 mm/min. After elongation, the clamp reverts to its starting position.Next, after a 5-minute wait, a second cycle is started. The permanentplastic deformation, which is expressed as the percentage permanentlyelongated, can be read from the second curve.

D. Determination of the tear resistance using an Elmendorf tester inaccordance with ASTM D1922.

E. Determination of the stress-strain properties in accordance with ISO1184:

a) the breaking stress (BS) in MPa, both in the longitudinal direction(LD) and the transverse direction (TD),

b) the elongation at break (EAB) in %, in the longitudinal direction LDas well as the transverse direction TD.

F. Determination of the softening point T₁ in accordance with thefollowing method:

A flat piece of thermoplastic polyurethane film is placed between twoquartz discs (diameter=5,8 mm) and introduced into the Mettler ThermoMechanical Analyzer TMA40. A quartz tubular probe connected to the LVDTposition sensitive detector is then positioned on top of the upper discwith a controlled constant load of 2N. After equilibration, thetemperature is increased from 30° C. to 250° C. at a rate of 10° C./min.During the temperature scan the probe position versus the sampletemperature is recorded. The onset of the change in probe position lineis indicated as the softening temperature.

The measurement is carried out in a helium atmosphere. Temperature andheight calibration occurs as specified in the Mettler manual.

EXAMPLE 1

Into a reactor of 1500 | were charged 40,7 kg of 4,4′-diphenyl methanediisocyanate (MDI) and, after flushing with nitrogen, heated to about80° C. Next, 44,8 kg of polyethylene oxide glycol having an averagemolecular weight of 2000 (PEG2000), which had also been heated to 80°C., were added slowly. Once all the PEG2000 had been added, 0,5 kg ofIrganox 1010® and 1 kg of Tinuvin 765® (both ex Novartis) wereincorporated into the reaction mixture, after which a mixture of 12 kgof 1,4-butane diol and 2,47 kg of propoxylated bisphenol A in the formof Dianol 320® (ex Akzo Nobel) was added rapidly and with good stirring.The resulting mixture was then immediately poured into a shallow mouldand after 24 hours of curing cut and ground up into a granulate in aknown manner and then processed into granules with the aid of atwin-screw (mixing) extruder. The softening point Tf of the thusobtained polymer A was determined by means of TMA to be 186° C.

Using an extruder equipped with a flat die this polymer was processedinto a 18 μm thick film.

EXAMPLE II (COMPARATIVE EXAMPLE)

In a manner analogous to that disclosed in Example I a polyurethane Bwas prepared, with the proviso that the Dianol 320® had been replaced infull by 1,4-butane diol.

The softening point of this polymer was 145° C.

This polymer was also made into a film having a thickness of about 20μm. The outcome of the measurements on the polyurethane films of ExampleI and the comparative example is listed in Table 1.

TABLE 1 Property Polyurethane B Polyurethane A (inv.) thickness in μm18.6 17.9 WVP in g/m² · 24 hr 2540 2555 WT in ml/m² · 24 hr 640 335 PPD% (permanent plastic deformation) LD 4.1 5.9 TD 3.9 5.9 tear resistancein N (calculated on film of 15 μm) LD 0.49 0.62 TD 0.48 0.70 breakingstress in MPa LD 35 29 TD 36 31 elongation at break in % LD 569 467 TD603 518 softening point T_(f), ° C. 145 186

The results listed in Table 1 clearly show that the waterproofness ofthe polyurethane film according to the invention is substantiallysuperior to that of the polyurethane film without araliphatic diol. Atthe same time, other physical properties such as the softening point andthe tear resistance in both the longitudinal and the transversedirection have also improved. Furthermore, the films according to theinvention exhibit far less adhesion on contact (sticking) than the knownpolyurethane films.

EXAMPLE III

In a manner analogous to that disclosed in Example I a number ofpolyurethanes having the following composition were prepared:

TABLE 2 PEG butane Dianol Dianol Tf adhesion 2000 MDI diol-1,4 320 ®220 ® TMA on Polymer wt. % wt. % wt. % wt. % wt. % ° C. contact C 44 4111 4 181 ++ D 42 41 10 7 196 ++ E 49 36 11 4 178 ++

The results listed in Table 2 clearly show the higher softening pointand the greatly reduced adhesion on contact (sticking) of thepolyurethane films according to the invention.

What is claimed is:
 1. Non-porous, waterproof film having a water vaporpermeability of at least 1000 g/m² day in accordance with ASTM E96-66(Procedure B), with the proviso that the water temperature is kept at30° C., while the ambient temperature is 21° C. at 60% RH, comprising athermoplastic polyurethane composed of a polyether glycol, apolyisocyanate, and a chain extender, at a ratio of NCO to activehydrogen atom of 0.9:1 to 1.2:1, wherein the polyurethane is a reactionproduct of a composition comprising a) 40 to 52 wt. % of a total weightof the composition of polyalkylene oxide glycol having an averagemolecular weight of 800 to 4000 and an atomic ratio of carbon to oxygenin the range of 2.0:1 to 4.3:1, with the proviso that at least 30 wt. %of the polyurethane is composed of a polyether glycol having an atomicratio of carbon to oxygen in the range of 2.0:1 to 2.4:1, b) 30 to 45wt. % of the total weight of the composition of 4,4′-diphenyl methanediisocyanate, and c) 5 to 20 wt. % of the total weight of thecomposition of a combined amount of 1,4-butane diol and an araliphaticdiol, both the 1,4-butane diol and the araliphatic diol being present inthe composition, with the araliphatic diol comprising 0.5 to 10 wt. % ofthe total weight of the composition and having the formula

wherein k=0 or 1, where if k=1, Y stands for a methylene orisopropylidene group, Q has the meaning of an H-atom or a CH₃-group,C₆X₄ has the meaning of a phenylene group wherein X is hydrogen or achlorine or bromine atom, and m and n is the same or different and standfor an integer≧1, with m+n≦10, wherein a) is not c).
 2. A non-porouspolyurethane film according to claim 1, wherein the molecular weight ofthe polyalkylene oxide glycol is in the range of 1000 to
 3000. 3. Anon-porous polyurethane film according to claim 1, wherein the weightpercentage of polyalkylene oxide glycol is in the range of 41 to
 50. 4.A non-porous polyurethane film according to claim 1, wherein the weightpercentage of 4,4′-diphenyl methane diisocyanate is in the range of 35to 42 wt. %.
 5. A non-porous polyurethane film according to claim 1,wherein the polyalkylene oxide glycol has an average molecular weight ofabout
 2000. 6. A non-porous polyurethane film according to claim 1,wherein in the araliphatic diol, k=1 and Y represents an isopropylidenegroup, while Q and X have the meaning of an H-atom and m and n=1.
 7. Anon-porous polyurethane film according to claim 1, wherein in thearaliphatic diol, k=1 and Y represents an isopropylidene group, while Qhas the meaning of a CH₃-group and X has the meaning of an H-atom and mand n=1.
 8. A non-porous polyurethane film according to claim 6, whereinthe araliphatic diol is present in an amount of 1 to 8 wt. %. 9.Rainwear comprising the non-porous waterproof film according to claim 1.10. A tent comprising the non-porous waterproof film according toclaim
 1. 11. A seat comprising the non-porous waterproof film accordingto claim
 1. 12. A mattress cover comprising the non-porous waterprooffilm according to claim
 1. 13. A shoe comprising the non-porouswaterproof film according to claim
 1. 14. Underslating for roofingstructures comprising the non-porous waterproof film according toclaim
 1. 15. A medical garment comprising the non-porous waterproof filmaccording to claim
 1. 16. A wound dressing comprising the non-porouswaterproof film according to claim 1.